1. Technical Field
Embodiments of the invention relate generally to power converters. Other embodiments relate to power converters with reduced commutation losses and electrical stresses.
2. Discussion of Art
Trains typically feature a number of cars that are pushed or pulled by a locomotive. The locomotive has traction wheels engaged with the track. In modern designs, electric wheel motors drive the traction wheels. The electric wheel motors are powered via electrical distribution from one or more engine-driven generators housed within the locomotive. The traction wheels and wheel motors can be reversibly configured, to also act as brakes for slowing the locomotive.
Similarly, in the mining industry, large off-highway vehicles (“OHVs”) usually employ electrically motorized wheels for propelling or retarding the vehicle. In particular, OHVs typically include a large horsepower diesel engine (or other engine) in conjunction with an alternator, a main traction inverter, and a pair of wheel drive assemblies housed within the rear tires of the vehicle. The diesel engine is directly associated with the alternator such that the diesel engine drives the alternator. The alternator powers the main traction inverter, in which semiconductor power switches commutate the alternator output current to provide electrical power to electric drive motors of the two wheel drive assemblies.
In both locomotive and OHV applications, solid state power converters are used to provide high voltage current from the generators or alternators to the wheel motors. Such power converters include inductive coils to step down the voltage as well as semiconductor power switches to commutate the current. Although the above-described applications are typical, it will be appreciated that power converters can be used in many other settings.
By way of example, an isolated bidirectional H-bridge converter may be utilized. This type of converter includes two full semiconductor bridges connected through a galvanic isolated power transformer. Such a converter can transfer power in both directions with voltages at the primary and secondary side varying within a range.
Isolated H-bridge converters may include power elements such as insulated gate bipolar transistors (IGBTs) that are switched on and off by drive circuitry in an alternating fashion to produce an output AC or other waveform. Other types of switchable semiconductor devices may also be used in the H-bridge circuit of such converters. These include power BJT transistors, power MOSFETs, integrated gate commutated thyristors (IGCT), gate turn-off thyristors (GTO), or any other device controllable semiconductor switched by a low power signal (e.g., gate signal). Switching under load, however, can lead to commutation losses and electrical stresses.
Therefore, it is desirable to reduce power converter commutation losses and electrical stresses to improve converter operation and efficiency.